08Flow-Field Particle Drift

<main class="stage">
<div class="pv is-demo" id="pvRoot">
  <canvas class="pv__canvas" id="pvCanvas" width="480" height="300"></canvas>
  <p class="pv__caption">A background where 80 particles trail color as they drift along a noise flow field</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-ink);

.pv {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.pv__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.pv__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 72%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 247, 230, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .pv__caption { font-size: 10px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .pv { cursor: default; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.pv {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.pv__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.pv__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 72%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .pv__caption {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .pv {
    cursor: default;
  }
}

(function () {
  // 기법: 2D 값 노이즈로 방향장(flow field)을 만들고, 입자 PLASMA_PARTICLE_COUNT 개가
  // 각자의 자리에서 그 방향을 따라 흐르며 지나간 자리를 옅게 남긴다(트레일). 트레일은
  // 매 프레임 살짝 페이드되는 offBuf 위에 누적되므로, 매 프레임을 독립 계산하는 다른
  // 항목과 달리 상태(입자 위치·트레일)를 이어간다 — reduce 에서는 이 상태 갱신 자체를 멈춘다.
  var root = document.getElementById('pvRoot');
  var canvas = document.getElementById('pvCanvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

  var CALC_W = 160, CALC_H = 100;
  var LOOP_MS = 2000;
  var PLASMA_PARTICLE_COUNT = 80;
  var PLASMA_FLOW_SCALE = 0.05;
  var PLASMA_SPEED_PX_S = 34;
  var PLASMA_FADE_ALPHA = 0.10;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () {
      s = (s * 1664525 + 1013904223) >>> 0;
      return s / 4294967296;
    };
  }

  function hslToRgb(h, s, l) {
    h = ((h % 360) + 360) % 360;
    var c = (1 - Math.abs(2 * l - 1)) * s;
    var x = c * (1 - Math.abs((h / 60) % 2 - 1));
    var m = l - c / 2;
    var r, g, b;
    if (h < 60) { r = c; g = x; b = 0; }
    else if (h < 120) { r = x; g = c; b = 0; }
    else if (h < 180) { r = 0; g = c; b = x; }
    else if (h < 240) { r = 0; g = x; b = c; }
    else if (h < 300) { r = x; g = 0; b = c; }
    else { r = c; g = 0; b = x; }
    return 'rgb(' + Math.round((r + m) * 255) + ',' + Math.round((g + m) * 255) + ',' + Math.round((b + m) * 255) + ')';
  }

  var NOISE_DIM = 40;
  var noiseRand = seedRand(417082);
  var noiseTable = new Float32Array(NOISE_DIM * NOISE_DIM);
  for (var ni = 0; ni < noiseTable.length; ni += 1) noiseTable[ni] = noiseRand();

  function noiseAt(xi, yi) {
    var wx = ((xi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
    var wy = ((yi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
    return noiseTable[wy * NOISE_DIM + wx];
  }
  function smoothstep(t) { return t * t * (3 - 2 * t); }
  function valueNoise2D(x, y) {
    var x0 = Math.floor(x), y0 = Math.floor(y);
    var tx = smoothstep(x - x0), ty = smoothstep(y - y0);
    var v00 = noiseAt(x0, y0), v10 = noiseAt(x0 + 1, y0);
    var v01 = noiseAt(x0, y0 + 1), v11 = noiseAt(x0 + 1, y0 + 1);
    var a = v00 + (v10 - v00) * tx;
    var b = v01 + (v11 - v01) * tx;
    return a + (b - a) * ty;
  }

  var off = document.createElement('canvas');
  off.width = CALC_W; off.height = CALC_H;
  var octx = off.getContext('2d');
  octx.fillStyle = '#0c0e16';
  octx.fillRect(0, 0, CALC_W, CALC_H);

  var pRand = seedRand(417083);
  var particles = [];
  for (var pi = 0; pi < PLASMA_PARTICLE_COUNT; pi += 1) {
    particles.push({
      x: pRand() * CALC_W,
      y: pRand() * CALC_H,
      hueSeed: pRand() * 360
    });
  }

  var flowT = 0;
  function stepSim(dtMs) {
    octx.fillStyle = 'rgba(12,14,22,' + PLASMA_FADE_ALPHA + ')';
    octx.fillRect(0, 0, CALC_W, CALC_H);
    flowT += dtMs * 0.00035;
    var dtS = dtMs / 1000;
    for (var i = 0; i < particles.length; i += 1) {
      var p = particles[i];
      var ang = valueNoise2D(p.x * PLASMA_FLOW_SCALE + flowT, p.y * PLASMA_FLOW_SCALE) * Math.PI * 4;
      p.x += Math.cos(ang) * PLASMA_SPEED_PX_S * dtS;
      p.y += Math.sin(ang) * PLASMA_SPEED_PX_S * dtS;
      if (p.x < 0) p.x += CALC_W; if (p.x >= CALC_W) p.x -= CALC_W;
      if (p.y < 0) p.y += CALC_H; if (p.y >= CALC_H) p.y -= CALC_H;
      var hue = (ang * 57.3 + p.hueSeed + flowT * 40) % 360;
      octx.fillStyle = hslToRgb(hue, 0.75, 0.58);
      octx.fillRect(p.x - 0.6, p.y - 0.6, 1.6, 1.6);
    }
  }

  var cw = 480, ch = 300;
  function fit() {
    var r = wrap.getBoundingClientRect();
    cw = Math.max(1, Math.round(r.width));
    ch = Math.max(1, Math.round(r.height));
    canvas.width = cw; canvas.height = ch;
    present();
  }

  function present() {
    ctx.imageSmoothingEnabled = false;
    ctx.clearRect(0, 0, cw, ch);
    ctx.drawImage(off, 0, 0, CALC_W, CALC_H, 0, 0, cw, ch);
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var playing = !reduce;
  if (reduce) {
    root.classList.remove('is-demo');
    for (var w = 0; w < 70; w += 1) stepSim(1000 / 30);
  }

  var lastTs = null;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = ts - lastTs;
    lastTs = ts;
    if (playing) {
      stepSim(Math.min(dt, 48));
    }
    present();
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  present();
  requestAnimationFrame(tick);
})();

import { useEffect, useRef } from "react";
import styles from "./PlasmaFlowParticleDrift.module.scss";

type Particle = { x: number; y: number; hueSeed: number };

export default function PlasmaFlowParticleDrift() {
  const rootRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    if (!root || !canvas) return;
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
    const wrap = canvas.parentElement as HTMLElement;

    // 기법: 2D 값 노이즈로 방향장(flow field)을 만들고, 입자 PLASMA_PARTICLE_COUNT 개가
    // 각자의 자리에서 그 방향을 따라 흐르며 지나간 자리를 옅게 남긴다(트레일). 트레일은
    // 매 프레임 살짝 페이드되는 offBuf 위에 누적되므로, 매 프레임을 독립 계산하는 다른
    // 항목과 달리 상태(입자 위치·트레일)를 이어간다 — reduce 에서는 이 상태 갱신 자체를 멈춘다.
    const CALC_W = 160, CALC_H = 100;
    const PLASMA_PARTICLE_COUNT = 80;
    const PLASMA_FLOW_SCALE = 0.05;
    const PLASMA_SPEED_PX_S = 34;
    const PLASMA_FADE_ALPHA = 0.1;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }

    function hslToRgb(h: number, s: number, l: number) {
      h = ((h % 360) + 360) % 360;
      const c = (1 - Math.abs(2 * l - 1)) * s;
      const x = c * (1 - Math.abs(((h / 60) % 2) - 1));
      const m = l - c / 2;
      let r = 0, g = 0, b = 0;
      if (h < 60) { r = c; g = x; b = 0; }
      else if (h < 120) { r = x; g = c; b = 0; }
      else if (h < 180) { r = 0; g = c; b = x; }
      else if (h < 240) { r = 0; g = x; b = c; }
      else if (h < 300) { r = x; g = 0; b = c; }
      else { r = c; g = 0; b = x; }
      return "rgb(" + Math.round((r + m) * 255) + "," + Math.round((g + m) * 255) + "," + Math.round((b + m) * 255) + ")";
    }

    const NOISE_DIM = 40;
    const noiseRand = seedRand(417082);
    const noiseTable = new Float32Array(NOISE_DIM * NOISE_DIM);
    for (let ni = 0; ni < noiseTable.length; ni += 1) noiseTable[ni] = noiseRand();

    function noiseAt(xi: number, yi: number) {
      const wx = ((xi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
      const wy = ((yi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
      return noiseTable[wy * NOISE_DIM + wx];
    }
    function smoothstep(t: number) { return t * t * (3 - 2 * t); }
    function valueNoise2D(x: number, y: number) {
      const x0 = Math.floor(x), y0 = Math.floor(y);
      const tx = smoothstep(x - x0), ty = smoothstep(y - y0);
      const v00 = noiseAt(x0, y0), v10 = noiseAt(x0 + 1, y0);
      const v01 = noiseAt(x0, y0 + 1), v11 = noiseAt(x0 + 1, y0 + 1);
      const a = v00 + (v10 - v00) * tx;
      const b = v01 + (v11 - v01) * tx;
      return a + (b - a) * ty;
    }

    const off = document.createElement("canvas");
    off.width = CALC_W; off.height = CALC_H;
    const octx = off.getContext("2d") as CanvasRenderingContext2D;
    octx.fillStyle = "#0c0e16";
    octx.fillRect(0, 0, CALC_W, CALC_H);

    const pRand = seedRand(417083);
    const particles: Particle[] = [];
    for (let pi = 0; pi < PLASMA_PARTICLE_COUNT; pi += 1) {
      particles.push({ x: pRand() * CALC_W, y: pRand() * CALC_H, hueSeed: pRand() * 360 });
    }

    let flowT = 0;
    function stepSim(dtMs: number) {
      octx.fillStyle = "rgba(12,14,22," + PLASMA_FADE_ALPHA + ")";
      octx.fillRect(0, 0, CALC_W, CALC_H);
      flowT += dtMs * 0.00035;
      const dtS = dtMs / 1000;
      for (let i = 0; i < particles.length; i += 1) {
        const p = particles[i];
        const ang = valueNoise2D(p.x * PLASMA_FLOW_SCALE + flowT, p.y * PLASMA_FLOW_SCALE) * Math.PI * 4;
        p.x += Math.cos(ang) * PLASMA_SPEED_PX_S * dtS;
        p.y += Math.sin(ang) * PLASMA_SPEED_PX_S * dtS;
        if (p.x < 0) p.x += CALC_W; if (p.x >= CALC_W) p.x -= CALC_W;
        if (p.y < 0) p.y += CALC_H; if (p.y >= CALC_H) p.y -= CALC_H;
        const hue = (ang * 57.3 + p.hueSeed + flowT * 40) % 360;
        octx.fillStyle = hslToRgb(hue, 0.75, 0.58);
        octx.fillRect(p.x - 0.6, p.y - 0.6, 1.6, 1.6);
      }
    }

    let cw = 480, ch = 300;
    function fit() {
      const r = wrap.getBoundingClientRect();
      cw = Math.max(1, Math.round(r.width));
      ch = Math.max(1, Math.round(r.height));
      canvas!.width = cw; canvas!.height = ch;
      present();
    }

    function present() {
      ctx!.imageSmoothingEnabled = false;
      ctx!.clearRect(0, 0, cw, ch);
      ctx!.drawImage(off, 0, 0, CALC_W, CALC_H, 0, 0, cw, ch);
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let playing = !reduce;
    if (reduce) {
      root.classList.remove("is-demo");
      for (let w = 0; w < 70; w += 1) stepSim(1000 / 30);
    }

    let lastTs: number | null = null;
    let raf = 0;
    function tick(ts: number) {
      if (lastTs === null) lastTs = ts;
      const dt = ts - lastTs;
      lastTs = ts;
      if (playing) { stepSim(Math.min(dt, 48)); }
      present();
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    present();
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      window.removeEventListener("resize", fit);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.pv} is-demo`} ref={rootRef}>
        <canvas className={styles.pv__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.pv__caption}>노이즈 흐름장을 따라 입자 80개가 색 궤적을 남기는 배경</p>
      </div>
    </main>
  );
}